The Astra GSi and SRi Turbo come equipped with the Z20LET engine producing 197bhp and 184lbft. The ECU is a Bosch ME1.5.5 setup.


At GCAP we have tried and tested tuning packages for this engine, below is a break down.



GCAP's bespoke custom ECU remaps will tweak the fuelling, boost, ignition timing, etc to boost the power to around 230bhp without any hardware modifications. We advise at this stage the addition of a panel filter or cone filter to allow the vehicle to breath better.


At this stage we now address the exhaust system and charge air cooling. By removing the restrictive system and fit a larger bored free flowing exhaust system, we again open up room for more power. The standard system is very restrictive, so by fitting a 2.75inch-3inch exhaust along with sports cat or decat system we allow for the car to remove the gasses more efficiently. To ensure a consistent performance figure, we swap the standard intercooler for an uprated front mounted cooler. Combined with a map tweak we see figures in the 240-250bhp area.


At this stage we swap out the LET standard turbo for the Astra H VXR k04 kkk unit. With an ECU calibration we see 250-270bhp.


At this stage we swap out the injectors for the Astra VXR injectors. This tied in with the FMIC, VXR K04 and exhaust system will see 300bhp and 330lbft.



At stage 5 we now remove the  K04 turbo and replace with a hybrid alternative. The hybrid turbos take the K04 KKK unit and replace the internals with:

  • High flow Billet K06 large trim Compressor Wheel

  • Re-profiled compressor housing

  • Modified turbine wheel blades to reduce backpressure

  • Lightening of turbine wheel for quicker response

  • 360 degree thrust kit

  • Unit fully blueprinted to motorsport tolerances

With this turbo we see power in around 320-360bhp. At this level of performance it is now important to forge the engine. There will be other supporting mods required such as bigger injectors, uprated clutch kit, LSD etc.



The next upgrade will be the camshafts. The inlet and exhausts camshafts are swapped out for GCAP spec fast road cams allowing the car to flow air far better due to the opening of the valves higher and longer.



If you wish to go further down the power route, the next option is installing a Garrett turbo. These range in performance and see anywhere between 350bhp-500bhp+. One of our demo vehicle is running 514bhp.


We offer full engine forging the Z20LEH and Z20LET engines.


On the LEH engines found in the Astra and Zafira VXRs, we offer a full strip down and rebuild service using FCP, ZRP or PEC conrods. The pistons themselves are forged from the factory so these only need a clean up and new pistons rings installed. However, we can offer Wossner pistons for this engine.

Included in the rebuild are all new gaskets top and bottom end, plus a full head rebuild including valve lapping, new stem seals, full degrease and skim. Customers have the option of upgrading the valve springs and stem seals whilst this is done.


For the LET engines, the rebuild is the same as the LEH but we offer the choice of LEH or Wossner pistons, balance shaft delete and the addition of under piston cooling.


We can offer a variety of suspension and handling upgrades spec'd to your exact needs, whether it be fast road or a full on track set up.


We can offer lowering springs, coil over kits, RARBs, FARBs, Uprated engine mounts and bushes.


We also offer a variety of clutch and flywheel set ups ranging from stage 1 - stage 3. Single mass flywheel conversion, uprated clutches, 4 and 6 paddle clutches and uprated covers. To help aid put the power dowe we also recommend the addition of a limited slip differential at any level of tune.


The Z20LET,LEL,LER and LEH engines all suffer from a problem with the stem seals. Like most engines, these have a valve stem which the valve runs in, which has the valve stem seal at the end of it to stop oil running down the stem. However, these engine's seals just push onto the end of the stem with nothing to hold them on but friction. Therefore high EGT'S, age and frequent hard revving results in them to pop off and cause leaky valve stems.

We offer 2 methods of repair, one with the head on, and one with the head off. With the head off you gain the extra service of valve lapping, new headgasket, skim and full head degrease and clean up.


We also offer uprated stem seal retainers. These are CNC machined from stainless steel, are 0.5mm thicker than the original spring seat for extra strength, plus they sit 1mm off the seals to allow for differences in stem fitments and are fatter in the base for a tighter tolerance fit in the head so they dont float around.



GCAP Performance

6 Powis Mews

Notting Hill


W11 1JN